python opencv (cv2) in blender
Today I found an easy way to start using OpenCV in Blender without any (manual) compilation steps. My OS is Ubuntu 18.04 (64bit) and I run Blender 2.79b. 

It may be also important to say, that I did not installed Blender from repository (e.g. apt), but simply downloaded the archive and extracted in a sub-folder of my home directory.

I performed following steps to start using OpenCV:


Open Terminal
Change directory (cd) to [blender]/2.79/python/bin
Executed ./python3.5m -m ensurepip (to become pip available)
Executed ./python3.5m -m pip install --upgrade pip (upgrade pip)
Executed ./python3.5m -m pip install opencv-python (Though an unofficial build the version I got was 3.4.2.17)
Executed ./python3.5m -m pip install opencv-contrib-python (I needed SIFT features and they are only available in the contrib package)


After these commands were executed I started Blender and performed a test where I extracted SIFT features from one Image and wrote an augmented result image to filesystem. Worked without issues.

It is that easy, that I would expect it somewhere to be written down in the internet, but unfortunately I have found only instructions which are far more complicated.

Hope this help someone!